1. Field of Invention
The present invention related to a method of forming a polycrystalline silicon film which forms a polysilicon film by crystallizing silicon by means of carrying out plasma exposure and applying an electric field thereon.
2. Discussion of Related Art
In view of performance, low temperature polysilicon, of which product cost is low owing to its low formation temperature and which also enables to provide an large-scale display area, is as good as high temperature polysilicon.
There are various methods for forming low temperature polysilicon such as solid phase crystallization(SPC), laser crystallization and the like.
Enabling to provide low temperature crystallization under 400xc2x0 C., which is disclosed in [Hiroyaki Kuriyama, et. al, Jpn. J. Appl. Phys. 31, 4550 (1992)], the laser crystallization fails to provide uniform crystallization and has difficulty in forming polysilicon on a substrate of a large area due to an expensive apparatus and low productivity.
When polysilicon is formed by solid phase crystallization, uniform crystallites are attained in use of an inexpensive apparatus. However, solid phase crystallization requires high temperature and long processing time of crystallization, which is hardly applied to forming polysilicon on a glass substrate.
A new method of crystallizing amorphous silicon at low temperature, which is so-called metal induced crystallization, is disclosed in [M. S. Haque, et. al, J. Appl. Phys. 79, 7529(1996)]. Metal induced crystallization crystallizes amorphous silicon by contacting amorphous silicon with a specific kind of metal which induces crystallization of silicon and then by carrying out annealing, thereby enabling to lower crystallization temperature.
In Ni-induced crystallization, crystallization is accelerated by the NiSi2 which is the final phase of Ni silicide and works as a crystal nucleus, which is disclosed in [C. Hayzelden, et. al, J. Appl. Phys. 73, 8279 (1993)]. As a matter of fact, NiSi2, of which lattice constant is 5.406 xc3x85 similar to 5.430 xc3x85 of silicon, has the similar structure of silicon. Thus, NiSi2 works as a crystal nucleus of amorphous silicon, accelerating crystallization to the direction  less than 111 greater than , which is disclosed in [C. Hayzelden, et. al, Appl. Phys. Lett. 60, 225 (1992)]. The crystallization of amorphous silicon is accelerated by metal species.
The metal-induced crystallization is affected by time and temperature of annealing as well as quantity of metal, of which crystallization time is lowered in general while the quantity of metal increases.
Metal induced crystallization has a merit of low crystallization temperature, unfortunately requiring long thermal process time over 20 hours at 500xc2x0 C. Therefore, this method has many difficulties in being applied to mass production of polycrystalline silicon.
As quantity of metal increases, so metal induced crystallization becomes effective. However, intrinsic characteristics of a silicon film are changed due to metal contamination in the crystallized silicon film.
As mentioned in the above explanation, MIC requires long thermal process time over 20 hours at 500xc2x0 C. for crystallization. Thus, it still requires high crystallization temperature and long process time.
As the amount of metal in the film increases, so does the effect of MIC as well as metal contamination. Such contamination causes the change of intrinsic characteristics of a silicon film.
Accordingly, it is very important to lower the time and temperature of thermal process of crystallization as well as reduce the metal contamination in the silicon film crystallized by MIC.
Accordingly, the present invention is directed to a method of forming a polycrystalline silicon film that substantially obviates one or more of the problems due to limitations and disadvantages of the related art.
The object of the present invention is to provide a method of forming a polycrystalline silicon film which lowers the time and temperature of crystallization.
Another object of the present invention is to provide a method of forming a polycrystalline silicon film which reduces the metal contamination in a crystallized silicon film by means of controlling plasma density and plasma exposure time.
Additional features and advantages of the invention will be set forth in the description which follows and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, the present invention includes the steps of forming a metal plasma exposure layer on a substrate wherein the metal plasma exposure layer works as a catalyst for metal induced crystallization, and depositing amorphous silicon on the substrate on which the plasma exposure layer is formed while an electric field is applied thereon.
In another aspect, the present invention includes the steps of forming a metal plasma exposure layer on a substrate wherein the metal plasma exposure layer works as a catalyst for metal induced crystallization, forming a first amorphous silicon film to a predetermined thickness on the plasma exposure layer, and depositing a second amorphous silicon on the substrate while an electric field is applied to the substrate where the plasma exposure layer and the amorphous silicon layer are formed.
In a further aspect, the present invention includes the steps of forming a metal plasma exposure layer on a substrate wherein the metal plasma exposure layer works as a catalyst for metal induced crystallization, and depositing an amorphous substance on the substrate where the plasma exposure layer is formed while an electric field is applied to the substrate, wherein silicide is generated from a reaction between the amorphous substance and metal of the plasma exposure layer as soon as the amorphous substance is deposited and wherein crystallization is induced by the silicide.
In a further aspect, the present invention includes the steps of depositing a first thin amorphous silicon layer on an insulating substrate, forming a metal plasma exposure layer on the thin amorphous silicon layer on the substrate while an electrical field is applied to the substrate where the amorphous silicon and the metal plasma exposure layer are formed, and forming a second amorphous silicon layer on the metal plasma and the first amorphous silicon layer in an electric field.
In a further aspect, the present invention includes the steps of depositing a first thin amorphous silicon layer on an insulating substrate in an electric field, forming a metal plasma exposure layer on the thin amorphous silicon layer on the substrate while an electrical field is applied to the substrate where the amorphous silicon and the metal plasma exposure layer are formed, and forming a second amorphous silicon layer on the metal plasma and the first amorphous silicon layer in an electric field.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.